Cataphoretically coated heater insulator assembly



April 1958 T. w. BLICKWEDEL EIAL 2,831,140

CATAPHORETICALLY COATED HEATER INSULATOR ASSEMBLY Filed Oct. 12, 1953 INVENTORS THEODORE w. BLICKWEDEL WILLIAM J; RHYNE Unit d ta es- Pateflt CATAPHORETICALLY COATED HEATER INSULATOR ASSEMBLY Theodore W. Biickwedel, Emporium, and William J.

Rhyne, Prospect Park, Pa., assignors to Sylvania Electric Products Inc., a corporation of Massachusetts Application October 12, 1953, Serial No. 385,484

Claims. (Cl. 313-340) The invention relates to heater construction and particularly to such construction where the heater is intended to be utilized in indirectlyheated cathodes in radio tubes.

At the present time it is necessary in many vacuum tube types to space the heater filament away from the enveloping cathode sleeve so that the tube will be able to withstand high heater-cathode voltages andmaintain low heater-cathode leakage values. In some cases this is effected by heavily insulating a wound or folded filament before inserting the same into the cathode sleeve. In other cases this is effected by cementing a coated heater filament into a specially formed ceramic piece and inserting the assemblage into the cathode sleeve. In still other cases a tungsten wire is coated with an insulating material and fired; the filament is then folded or wound and inserted into an insulation coated metal coil; then the two are inserted into the cathode sleeve. These methods and means are all objectionable in that they are expensive or require some form of spacer discrete from the heater between the heater and cathode sleeve to prevent looseness of parts.

It is an object of this invention to make a heater wherein the filament and insulating material surrounding the same form an integral unit and in which, during part mounting operations, they can be handled as a single piece and which combined structure has no loose parts capable of slipping out of position or of vibrating in the finished tube.

It is a further object of the invention to form an insulated heater which shall require less ceramic material than is conventionally required, thereby providing for usage of less ceramic, faster warm-up of the radio tube in which the heater is utilized and yet have the heater insulation contact the cathode to provide for better heat transfer to the cathode.

These and other objects will appear after reading the following specification and claims in conjunction with the accompanying drawings in which:

Fig. 1 is a view of an insulated heater inserted into a wire coil.

Fig. 2 is a view of the assemblage of Fig. 1 after the assemblage has been treated catephoretically, and

Fig. 3 is a view of an indirectly heated tube with our improved filament in the cathode sleeve.

Referring to the drawings with greater particularity there is disclosed in Fig. 1 a heater wire or filament 11 having a conventional insulating coating 13, for example of alumina, the filament being repeatedly folded and doubled on itself to form a heater wire of requisite resistance.

This wire so insulated and folded is next inserted in a coarsely coiled bare wire 15 and the whole lowered into a coating suspension having insulating properties and prefably of the same material as the coating on the filament. For the purpose of electrophoretically coating the wire 15, electrical contact is made to the wire coil 15 at either end of the coil but preferably at the end adjacent to the bare legs of the filament and, if desired additionally to coat r K 2,831,140 Patented Apr. 15., 1958 the filament, connection is also made to a bare leg of the filament. Current may be caused to fiow through the suspension and wire, or wire and filament, by applying an electrode to a metallic tank which houses the suspension. Upon current flow through the circuit, the bare coil of wire 15 is electrophoretically coated as shown at at 17 in Figure 2, to the desired diameter so as to snugly fit within a cathode sleeve, this being effected by varying the time of current flow or magnitude of potential applied to the circuit terminals. When the completed tube is in operation, the heating filament 11 only, is in the heater circuit, the coil 15, 17 acting only as a rigidifying and spacing element and occupying the space between the filament 11, 13 and the cathode sleeve. If, during manufacture, contact is made to a filament leg as described above, bare portions of the filament, such as cracks developing at the bights of the coated filament during bending, will be heavily coated also. But whether or not the filament is made part of the circuit, some particles of the bath will be gravitationally deposited on the filament insulation and filament. The coating on the bare wire 15 will blend into and adhere to the coating on the filament wire forming an integrated structure therewith, resulting in better heat transfer than where an insulated heater is merely thrust into an insulating sleeve.

After the wire 15 has been coated to the extent desired, it is removed from the coating bath, rinsed to remove any excess suspension, and dried, preferably by being placed in the path of a stream of warm, dry air. The coating on the wire 15 now clings to the coating on the filament, the coatings forming a unit, by nature of the dried coating particles. After drying, the unit is tired to sinter the insulator coating particles into the particles on the coil 15 effecting a fusing or bonding together of the insulator particles on the coil and those on the filament. The so formed unit is next thrust into a cathode sleeve, such as sleeve 19, and then the cathode assembly is mounted and placed in a vacuum tube 21, see Figure 3, in the customary manner.

Having thus described our invention, what we claim is:

1. Steps in the method of forming a well insulated heater filament comprising, inserting a folded heater filament with insulation thereon into a bare coil of wire to form an assembly, immersing the assembly in a coating bath, withdrawing the assembly comprising the coated filament and now coated coil of wire from the bath, and inserting the coated assembly into a cathode sleeve.

2. Steps in the method of forming a well insulated heater filament comprising inserting a folded heater filament with insulation thereon into a bare coil of wire to form an assembly, immersing the assembly in a coating bath, applying a coating to the bare wire and to a less extent to the filament while in said bath, withdrawing the assembly comprising the coated coil of wire and coated filament from the bath, and inserting the coated assembly into a cathode sleeve.

'5. Steps in the method of forming a well insulated heater filament comprising inserting a folded heater filament with insulation thereon into a bare coil of wire to form an assembly, immersing the assembly in a coating bath, applying a coating to the bare wire and to a less extent to the filament while in said bath, withdrawing the assembly comprising the now coated coil of wire and coated filament from the bath, drying the so withdrawn assembly, and inserting the coated assembly into a cathode sleeve.

4. Steps in the method of forming a well insulated heater filament comprising inserting a folded heater filament with insulation thereon into a bare coil of wire to form an assembly, immersing the assembly in a coating bath, applying a coating to the bare wire and to a less extent to the filament while in said bath, withdrawing the assembly comprising the now coated coil of wire and coated filament from the bath, drying and sintering the so withdrawn assembly and inserting the coatedassembly into a cathode sleeve.

5. A heater construction comprising an insulated wire filament, an outer coil surrounding substantially the full length of said insulated wire filament, and a continuous insulating coating covering said outer coil and embracing said insulated filament at the points of contact of said outer 10 '4 coil with said filament, thereby bonding said outer coil substantially throughout its length to said insulated filament.

References Cited in the file of this patent UNITED STATES PATENTS 1,975,870 Shrader Oct. 9, 1934 2,247,869 Beers July 1, 1941 2,753,480 Batzle et al. July 3, 1956 

